In most mast and sail arrangements, whether for sailboats, iceboats or other devices, such as windmills, which utilize wind power, a sail is presented to the wind. Controlled amounts of sail area also must be easily changeable for varying wind conditions.
Conventional sails used on sailboats have only a single sheet which is drawn into the shape of an airfoil by the force of the wind. The amount of sail available for sailing can be roughly controlled by the distance the sail is hoisted up the mast. As a practical matter, however, the distance which the sail is hoisted up the mast usually remains constant while sailing since the conventional sail should be fully extended vertically when sailing. The effective conventional sail area is controlled by varying the angle the sail presents to the windstream.
Various sail furling mast constructions are known in which sails can be rolled around a mast core or sleeve. In previous constructions, however, the portion of the sail which is free joins the rolled-up portion of the sail at a tangent to the mast sleeve.
What is needed, then, is a sail furling apparatus which has a separated double sheet sail which may be rolled through a forward portion of a freely rotatable eccentric sheath.